Liquid crystal display panels include, for example, a TFT array substrate on which a thin film transistor (hereinafter also referred to as “TFT”) is provided for each sub-pixel as a minimum unit of an image, a counter substrate facing the TFT array substrate, and a liquid crystal layer provided between the TFT array substrate and the counter substrate.
The TFT array substrate includes, for example, a plurality of gate lines extending in parallel to each other, a plurality of capacitor lines each provided between the gate lines and extending in parallel to each other, a gate insulating film which covers the gate lines and the capacitor lines, a plurality of source lines provided on the gate insulating film and extending in parallel to each other in a direction perpendicular to the gate lines, a plurality of TFTs provided for each of the intersections of the gate lines and the source lines, an interlayer insulating film which covers the TFTs and the source lines, and a plurality of pixel electrodes provided in a matrix pattern on the interlayer insulating film and connected to a corresponding one of the TFTs.
Each TFT includes, for example, a gate electrode provided on a transparent substrate, such as a glass substrate, a gate insulating film which covers the gate electrode, an island-shaped semiconductor layer provided on the gate insulating film so as to overlap with the gate electrode, and a source electrode and a drain electrode provided on the semiconductor layer so as to be apart from each other. Here, the gate electrode is a laterally protruding portion of the gate line. The source electrode is a laterally protruding portion of the source line. The drain electrode is connected to the pixel electrode via a contact hole formed in the interlayer insulating film, and comprises an auxiliary capacitor by overlapping with the capacitor line via the gate insulating film.
In the liquid crystal display panel, the source electrode and the drain electrode of the TFT provided for each sub-pixel may be short-circuited if, for example, conductive foreign substances or film residues intervene between the source electrode and the drain electrode. If such an event occurs, a display signal from the source line is input to the pixel electrode of that sub-pixel all the time, and the sub-pixel is easily detected as a bright spot. Thus, at the sub-pixel detected as a bright spot, a defect repair is performed to turn the bright spot into a black spot by, for example, disconnecting the drain electrode and connecting a side of the disconnected drain electrode which is connected to a pixel electrode, with the gate line or the capacitor line.
For example, Patent Document 1 discloses a method for repairing a faulty pixel in a TFT type liquid crystal display device in which a data signal (a display signal) is not applied to a pixel electrode of the faulty pixel from a data bus line (a source line). According to the method, a portion of a TFT gate electrode which is connected to a gate bus line (a gate line) is irradiated with optical energy, thereby electrically connecting the gate electrode and the pixel electrode of the faulty pixel via a drain electrode, and applying a scan signal of the gate bus line to the pixel electrode of the faulty pixel.
In the repair method in which a drain electrode and a gate line are electrically connected to each other as disclosed in Patent Document 1, a bright spot may not sometimes be turned into a black spot, but detected as a half tone, depending on tone characteristics of the liquid crystal layer. Thus, a method in which a drain electrode and a capacitor line are electrically connected to turn a bright spot into a black spot is a mainstream repair method in fabricating liquid crystal display panels.